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course Phy 202
3/14 122.16.11
110216 physics
`q001. A BB of mass .12 g is shot at 80 m/s into the space between two tiles. The tiles are separated by 15 cm.
If the BB continues bouncing back and forth between the tiles for 2 seconds, without losing any of its speed, what average force does it exert on each tile?
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Fave=5 N
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How would the result change if the tile separation was reduced to 5 cm?
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Fave=16 N
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How would the result change if the BB was fired into a slightly irregular tile-lined 'box' approximately 5 cm on a side?
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After asking you, you said the force was 1/3 that of on regular tile-lined. Therefore it would approx 5.4 N.
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What does this question have to do with the kinetic theory of gases?
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You answered this for me—if we use particles bouncing back and forth, they collide so the velocities are equally distributed in the 3 directions.
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Optional problem: If the BB loses 10% of its momentum with each collision, what average force does it exert over the first 10 round trips? General College Physics students can use estimates, as can University Physics students. However University Physics students should consider applying calculus and/or differential equations.
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`q002. A wave is observed to travel down a rubber band chain of length 2.5 meters, making seven round trips in 10 seconds. What is the propagation velocity of that wave?
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C= 3.5 m/s
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By sending alternate pulses down the chain on alternate sides, a standing wave is created with a single antinode, located halfway down the chain. How much time must elapse between the pulses?
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35 m /10 s=3.5 m per every second of time. If a wave is 5 m from peak to peak (assuming that 1 antinode) then 5 m/3.5 m/s= 1.4 s
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How many pulses are sent by the time the first disturbance reaches the end of the chain? What is the shape of the chain at that instant?
The pulse rate is increased until the standing wave contains two antinodes, with a node in the middle. How much time must elapse between the pulses?
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Two pulses are sent before the first reaches the end of the chain; the shape, the one pulse is nearing the end of the chain as the second one is sent.
The wavelength will then be 2.5 m, then 2.5 m/3.5 m/s= .7 s
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How many pulses are sent by the time the first disturbance reaches the end of the chain? What is the shape of the chain at that instant?
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The first reaches the end before the next pulse is sent. The one pulse starts traveling back as the second starts to travel out.
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If a complete cycle consists of two alternate pulses, then in each case, how many complete cycles of the wave correspond to its length?
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`q003. Suppose the tension in a rubber band chain is 1 Newton for every 10% change in its length. If our chain has length 2.5 meters when under a tension of 1 Newton, then what will be the tension when its length is 2.7 meters, what will be the tension at length 3 meters, and at what length will the tension be 5 Newtons?
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At 2.7 meters, the tension will be 2 N
At 3 meters, the tension will be 3 N
At 5 meters, the tension will be 11 N.
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If the speed of the wave is c = sqrt( T / (m/L) ), then what is (m / L) for our chain (use also the information you obtained in the preceding question)?
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C=3.5 T = 1 Newton
m/l= T/c^2
m/L = 1 N/3.5 m/s^2=1 N/12.25 m^2/s^2=.08 kg/m
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What will be the wave speed at length 3 meters?
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C=sqrt (3 N/.08 kg/m)=6.12 m/s
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At length 3 meters, how frequently should pulses be sent in order to create the fundamental mode of vibration (the one with a single antinode)?
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In order to create a single antinode, then pulses should be sent every half second. 3 m/6.12 m/s=.49 s
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`q004. BB data: Shot at the same trajectory the BB follows a path similar to that of a good sand wedge shot in golf, but I believe it starts out with greater velocity and loses speed more quickly. In the sunlight against a blue sky you can track the thing for just about its entire flight. Pretty neat. Shot at the Moon, without correcting for gravity, and didn't really miss it by all that much. Don't want to steal NASA's thunder to I'll leave it at that. Shot into water at a low enough trajectory it will skip without losing too much speed (note: you generally don't want to shoot a gun at water because the bullet could 'skip' with dangerous consequences; I have a high bank on the opposite side). Shot at a nearly vertical trajectory the water stops it within a few centimeters. All this appears to be consistent with the gun's rating of 0.3 Joules and the BB's .12 gram mass (which is in turn consistent with the 250 ft/sec muzzle velocity). At that speed the BB should climb for about 1000 feet, if shot in a vacuum, which is what leads me to believe it's losing velocity.
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&#Your work looks good. See my notes. Let me know if you have any questions. &#